Iron Heart
by Paulzies
Summary: Being not dead was nice. Being stuck in another world where everybody but him had superpowers?...Not so much. Still, he was going to find a way back home to see Pepper and Morgan. He'd solved time travel in three days, so inter-dimensional hopping should be a piece of cake. They'd made a promise, hadn't they? "Whatever it takes." AVENGERS ENDGAME SPOILERS
1. Chapter 1

**A/N: SPOILERS FOR ENDGAME. DO NOT READ IF YOU HAVE NOT WATCHED AVENGERS ENDGAME**

**Prologue:**

_"You can rest now, Tony."_

Against all of his expectations and calculations, Tony Stark opened his eyes once more. The last thing he remembered was Pepper crouching in front of him, wearing the suit he'd painstakingly made for her.

Well, that was one good thing that came out from all this, he supposed. Pepper had finally worn the suit.

If only she hadn't been crying.

It didn't matter. He was alive, and he could see her again.

He furrowed his brows as he thought about it.

That should've been impossible. He'd crunched the numbers dozens of times. The sheer amount of radiation released during a _Snap _would poison a normal human being and kill them within minutes.

Which was why he hadn't bothered volunteering to do it in the first place. Thor and Banner were far more suitable candidates, and the last he'd seen, the Invincible Hulk had basically lost the use of his arm afterwards.

Outside of his suit and the Arc Reactor stuck on his chest, Tony Stark was an ordinary man.

He should _not _have survived, period.

But here he was.

Where the hell was _here_, anyway?

A grunt escaped his lips as he stood up in the narrow and nondescript alleyway he'd woken up in. He was getting old, alright. No more hero work after this. He brought a hand in front of his face. There were no signs of the stones. That was a good thing...he hoped.

He grimaced at the mere thought of it. In that fraction of a second where he had snapped his fingers, Tony Stark had been _God_. The secrets to the universe and all the power in the world had been concentrated into his right fist. Erasing Thanos and his army from existence had been easier than _breathing_.

In that moment, he could have wished for anything and everything.

And he kind of had. Now, he understood why Thanos had called them a forbidden temptation and destroyed them after getting a taste of their power.

Tony Stark also distinctly remembered wishing for one more miracle. Something that would let him see Morgan and Pepper one more time.

Well, here he was.

That was easier than he'd thought.

For a moment, Tony Stark basked in the air he was breathing. He missed the sound of a city. The honking of cars. The chattering seas of people as the sounds of their footsteps filled the air. Even the once-annoying clanking noises of construction sites building new skyscrapers was music to his ears.

He hadn't heard this in a long time, and Tony Stark relished in the sound of victory.

He'd won.

_They'd _won.

Earth-no, the whole universe-was saved.

That was enough charity for a lifetime, wasn't it?

He stuck his hand into his pockets.

Where the hell was his phone? And his wallet?

Goddamn it, someone had freaking robbed _Iron Man_ while he was passed out in an alley.

Alright. That was new. But it wasn't anything that he couldn't solve. He still had his suit, after all.

"F.R.I.D.A.Y.,call Pepper."

"Yes, Mister Stark." The sound of his A.I. replying caused Tony Stark to feel a tad impatient, and he tapped his feet as he waited for the sound of a ringtone to start playing in his earpiece.

Still though, how'd he end up from the rubble of the Avengers Base to...he looked at an old newspaper on the floor...

_Japan_? He recognized the oriental language and the squiggly patterns. Not that it actually gave him any of the answers he was _really _looking for.

Never mind, Pepper could answer them, hopefully. You know, if F.R.I.D.A.Y. would actually call her already.

This was taking too long.

"Did you forget Pepper's number? If you need it I have it memorized, since I'm such an amazing husband and father," he remarked to the A.I. after a few more seconds of silence.

"Apologies, Mister Stark. I seem to be unable to connect to the call. The telecommunication frequencies here seem to be..._incompatible_ with the suit."

Tony Stark blinked. "I built you to be able to hack into military satellites."

"I am unable to access any of them either."

Well, wasn't that just inconvenient? The suit couldn't have been _that_ badly damaged. Unless...oh, right. The Infinity Stones. If there was anything that even his self-repairing and self-upgrading nanotechnology couldn't keep up with, it would be those six shiny pop rocks.

Okay. Still not unsalvageable.

He could always _fly _home.

But that would take hours.

Borrowing a phone to call Pepper seemed like a far better idea. Sure, it would rack up overseas charges, but hell, there had to be _someone_ willing to pay that in exchange for a chance to take a selfie with _Iron Man_.

It was a good plan.

Too bad the building next to him exploded.

Instead of tearing flesh and breaking bone, concrete chunks and debris harmlessly bounced off iron skin as Tony Stark felt the cold metal envelope his body. His vision became tinted and artificial as the suit's Heads-Up-Display activated. A glance to the corner of the HUD indicated that the suit was operating at 100% functionality. So his suit was working fine. Odd. Everything seemed to be in order, so why couldn't he get reception to make a simple phone call?

The figure towering over him made Tony Stark reconsider his priorities for the moment.

That wasn't Ant Man.

But there was no way a human could get this big without Pym Particles being involved. This guy had to be at least 10 stories tall.

Tony Stark flew up.

"Hey, Gulliver!" he shouted, the suit's built-in amplification system magnifying his voice.

The man turned around to face him, an ugly sneer on his face.

Tony Stark wasn't _exactly_ sure how the Pym Particle functioned, given that he hadn't exactly had a lot of time to play around with what few samples Scott Lang had with him. But he was quite certain that the whole shrinking and gigantification thing couldn't be done without a specialized suit.

The guy in front of him was clearly wearing jeans and a torn vest big enough that they could protect the modesty of a low-rise building.

"I didn't know Uniqlo stocked clothes larger than 'XXL'. Just how many 'X's did you ask for?"

The man only looked confused, and Tony Stark reminded himself that he was in Japan. English didn't quite cut it here.

Without any instruction, F.R.I.D.A.Y. played back whatever he had said in Japanese. AIs were useful like that.

In response, the giant picked up a parked car from the street and hurled it at him.

He activated his lasers, cutting the car in half near-instantly. As both halves sailed past him, Tony Stark reassessed his judgement of the man.

Just because he had the same ability as Ant Man didn't make this guy a hero too. In fact, the crowds of people running away while screaming pointed to the fact that Tony Stark had unknowingly confronted a bad guy.

Well, there went his retirement plan.

"_Who the hell are you, flying metal man?" _He didn't initially understand the man's garbled-sounding words, but F.R.I.D.A.Y.'s translation software quickly displayed the meaning on his HUD.

Tony Stark was surprised. Well, he _was_ halfway across the globe. Maybe the Avengers weren't that famous over here.

The words still felt fresh in his mouth.

"I am Iron Man."

**A/N: I just really needed to write this after watching Endgame. Heroes never die. Marvel might have you killed you off Tony Stank, but you'll always live on in our thoughts and hearts. **


	2. Chapter 2

**A/N: SPOILERS FOR ENDGAME. DO NOT READ IF YOU HAVE NOT WATCHED AVENGERS ENDGAME.**

**Still a short chapter, basically just Tony trying to figure wtf is going on. Also, I've watched the BnH movie, and I see alot of potential in bringing I-Island into this story.**

**Also, it's kind of ridiculous how I've managed to gain 150+ likes on SB forums and 200+ Follows on FF with just 1.3k word prologue.**

**Chapter 1:**

"If you throw another Ferrari at me, I'm going to lose it, big guy."

Tony Stark liked cars. He _really_, _really_ did. And every time he had to blast one away or laser it in half, a small part of him mourned at the loss.

In response, Not-Ant-Man sent a Mazda convertible sailing towards him. He took a few moments to admire his reflection in the well-polished bonnet of the car, before a repulsor beam sent it crashing into the building next to him.

It left a bad taste in his mouth. The owner of the car had clearly taken very good care of it.

"All right, play time's over, Super-Size Me." He increased the strength of his thrusters, flying higher than the giant was tall. From the corner of his eye, he spotted a helicopter approaching fast. Any hope that the authorities had arrived was crushed when the door slid open and the only thing pointing out was a giant camera.

Of course the press would arrive before the police.

The giant swung a hand at him, and Tony scoffed. Iron Man wasn't a fly that could be so easily swatted away. He raised both hands, shooting off a pair of repulsor attacks at maximum intensity.

Tony was surprised at how well they worked. The giant immediately recoiled, stumbling backwards and crushing a few homes, yelling out in pain. Steam hissed from his palms where the energy beams had melted skin.

So, Not-Ant-Man may have been bigger than the Hulk, but its constitution was nowhere near as durable. What a comforting revelation.

That, and well, after fighting Thanos, he was pleased that his weapons actually harmed his opponent on the first try.

"There's more where _that_ came from," he declared, waiting for a few moments for F.R.I.D.A.Y. to translate and broadcast it in Japanese. "So let's skip all the blood and gore and keep this PG, yeah? Surrender peacefully."

Inside his mask, he sighed. If only things could be so easy. Bad guys never gave up without a fight, and-

The sight of the villain turning around and running in the opposite direction made Tony blink. Was his opponent...running away?

"You know I can fly as fast as a jet fighter, right?" he hollered out. "Escape is futile!"

The giant ignored him, leaping over buildings like they were mere hurdles, and he quickly gave chase.

"Prepare to activate facial recognition, if he shrinks down to human-size in a crowded place, we won't have much time to find him," he instructed his F.R.I.D.A.Y..

"Affirmative, Mister Stark."

He wasn't going to let this guy escape. Pym Particles were too dangerous to be left in the hands of a villain. It wasn't just the size-changing ability, but if word of their time-travel capabilities ever got out...

Tony Stark stopped himself right there. He was just about to bring his feet together to form the combined thruster when something on his HUD caught his eye.

The giant was running towards a train depot, but he wasn't alone. Tony saw the newcomer standing calmly on a parked train carriage.

"Groot?"

He'd seen the sentient tree only once, in the final battle against Thanos, minutes before he'd performed the Snap. But the snarky talking raccoon hadn't been able to shut up about his friend while they had worked together, and Tony felt like he'd known the walking piece of wood his whole life.

The being standing on a train looked kind of different. Tony distinctly remembered Groot being naked the last time round. But hey, how many walking trees were there on Earth?

Groot raise an arm. Tendrils of wood exploded from his fingertips, forming a makeshift net just in time for the giant to run shin-first into it.

Tony slowed down. This he had to enjoy. Because the giant was so big, everything he did seemed to appear in slow motion.

The way his face contorted with surprise and pain as he realized he was tripping.

The way his arms started to flail wildly as he tried regain his balance.

Even the way his cheeks got smushed when the giant boot collided with his face and-

Wait what?

_"Canyon Cannon!"_

Another one? And what kind of clothes was she wearing?

"F.R.I.D.A.Y., am I seeing things or is there really a second giant drop-kicking the first giant?" It was exactly as he said. The new blonde giant wore a tacky-looking costume, and Tony felt his jaw drop when her kick sent the first Giant flying backwards.

"That is indeed the case, Mister Stark."

"She's in spandex," he said in amazement. Which meant that the second giant's costume hugged her admittedly-attractive figure like a second layer of skin. But Tony was sure he was only staring at her because she was, well, taking up half of his field of vision anyway. "Only good guys wear spandex, right?"

"Would you like me to cross-check with existing records of criminals?" the A.I. asked.

"No, that's okay."

No, actually it wasn't. Nothing was okay. What, did it rain Pym Particles recently?

The first, evil giant crashed to the ground, a giant bootprint etched into his face as his eyes rolled over in unconsciousness. His giant figure immediately began to shrink, and Tony noted with curiosity that his clothes shrank with him. Wouldn't that be something Banner would be interested in knowing about?

The female giant immediately raised a thumbs-up towards the news helicopter.

_"Don't worry everyone. Mount Lady has saved the day!"_

Mount Lady? Talk about a cheesy hero name.

He flew closer to her as she returned to the size of a regular human being.

"Hey, you!" he called out, his mask melting back into the rest of his suit. "Where'd you get Pym Particles?"

Both Mount Lady and Groot looked up at him in confusion. A second later, F.R.I.D.A.Y. translated his words into Japanese, and their confusion didn't seem to abate in the slightest.

_"Pym Particles? What's that?" _Mount Lady asked.

_"And who are you?" _Groot asked.

Tony blinked. "No that's wrong." He pointed to the wooden man. "You can only say 'I am Groot'. That's what the raccoon said." Then he pointed to Mount Lady. "You don't know what Pym Particles are?"

Mount Lady tilted her head in puzzlement, while Groot only looked even more mystified.

"Wait. You guys don't know who I am?"

They both shook their heads.

"I'm Iron Man. Tony Stark. Savior of New York. And the World. Also, owner of Stark Industries?"

_"Oh, an American Hero. I'm sorry, I don't recognize many of you. But thank you for your assistance,"_ Groot (but Tony was starting to think that the tree-man before him wasn't actually Groot) said, giving a small bow.

Was he serious? The Chitauri Invasion? Stark Industries? Him _saving the universe_ from Thanos? How could they have never heard of him? Come on, Ben & Jerry's named a flavor after him!

But then again...he'd never heard of _them_ either.

"You've got to at least have heard of the Avengers, right?"

They looked to each other.

_"The Avengers? Is that like...a band?"_ Mount Lady asked.

This...this felt a little familiar, and Tony Stark wasn't sure why.

"You know what, just forget it," he said. So the rumors about Japan living in its own little world were true after all. "Just tell me how you grew so big."

_"It's my Quirk,"_ she said, as though it was obvious.

Tony had to re-read the translation a few times. "F.R.I.D.A.Y., what exactly does your translation mean?"

"I have no idea, Mister Stark. The actual literal translation of what she said made even less sense, would you like to see it?"

"Yes."

_'It's my personality,'_ the updated translation read.

"Okay," Tony said, taking a deep breath. "That makes even less sense."

"I did warn you, Mister Stark."

"I'm sorry, Quirk?" he asked Mount Lady. Did that mean Pym Particles weren't involved? That was even more ridiculous. Without the Pym Particle, how the hell could she go about violating the law of Conservation of Mass?

_"Ah. I don't know what they call it in English. You know the thing that gives you super powers?"_

What thing? Was there such a thing? Banner basically got an overdose of gamma radiation, while Capt got pumped up with steroids. Thor was...well, an alien. There wasn't a single common thread between them that explained their powers.

_"By the way, we haven't introduced ourselves. I'm Mount Lady, while this," _she gestured towards Groot, _"is Kamui Woods. Nice to meet you...uh..." _

So it wasn't Groot after all. That was a bummer. He was hoping at least something could make sense today.

"Iron Man," he reminded her curtly. He'd literally introduced himself less than a minute ago.

_"That's a very cool-looking costume you have, Mister Iron Man. If you don't mind me asking, what kind of Quirk do you have?" _Kamui Woods asked.

"First off, it's not a costume, it's a _suit_. Second, I still have no idea what you're talking about."

_"What kind of power do you have? Removing the capabilities your...suit, what abilities do you_ _have?"_

Talk about a throwback. "I'm a genius, billionaire, playboy, philanthropist," he answered without hesitation.

_"Wait, you're rich?" _Mount Lady asked immediately.

Before he could respond, the wail of a siren cut him off.

_"You seem like you have many questions. Perhaps asking the police might help,"_ Kamui Woods said as a trio police cruisers pulled up right in front of them.

Oh yeah, Tony had a _ton _of questions. A whole list of them, actually.

The door of the lead car opened, and someone stepped out.

And another new question just got added to the very top of said list.

"Is that a _dog_." He pointed at the police officer. "_Wearing a suit_?"

His eyes had to be betraying him. There was no way it was true. An honest-to-God Beagle the size of a human wearing a three-piece, black-tie, suit.

The dog raised a paw to his chest and gave a small bow. _"I am Police Chief Tsuragamae Kenji."_

"And he _talks_?"

"Yes, I talk," the dog replied in fluent English. "I see that you are not a Japanese Hero. Allow me to thank you then, on behalf of our country, for your assistance in stopping the Villain."

Even as he spoke, the other police officers that had come with him were dragging the knocked-out giant-turned-back-human into one of the other police cruisers. He appreciated that one of them jabbed what looked like sedatives into the villain to keep him unconscious.

But other than that, Tony had no response. A bilingual dog. Wait, if the dog could bark, would that make him tri-lingual? Okay. Something definitely weird had happened after he'd done the Snap.

Rocket was a cyber-genetically enhanced scientific experiment made by alien races. _That_ he could somewhat accept. But Tony had a feeling that this wasn't the case here, unless Earth's technology had advanced so radically in the few...

He hesitated. Just how long had he been passed out?

"I'm sorry, but do you have the date?"

"It's March 26th."

Tony blinked. That couldn't be right. Last he remembered, it was April. Unless he'd gone back in time...

No, that couldn't be possible either. The lively city around him wouldn't exist.

Which meant that he'd gone _forward_.

"What year is it?"

"Um." The dog sounded surprised at the question. "It's 2142."

Oh, God damn it. Now he _really _wished that the Villain or Mount Lady had some Pym Particles on them.

**XxXxXxXxXx**

"How's it going, F.R.I.D.A.Y.?"

"The suit has now been reconfigured to possess telecommunication abilities. I'm working on trying to establish a secure connection with the Internet. Satellite uplink capabilities are still nonexistent."

So now he could call people. Which was good, if he even had anyone to call. It was the middle of the 22nd century. Everyone he knew had to be dead. Pepper would have died almost a century ago, and he doubted even Morgan could live until the ripe old age of a hundred twenty something. His only hope was Thor, who...probably still didn't have a cellphone.

The only thing he didn't understand was _how _he'd ended up time travelling into the future. It couldn't have been the Snap. He had vivid memories of the moments after it. Somebody had to have done something to him when he'd passed out.

Well, he'd find out soon. Once his suit had web-surfing capabilities, he was going get all the information he wanted.

In the meantime...

Tony Stark sat down and and brushed his fingers against the keyboard in front of him. He was surprised, that even after more than a century, public libraries existed. And that computers still had press-button keyboards. Even he'd moved on from them, and that was more than a hundred years ago

He had come here after the whole giants-and-talking-dog thing. The Police Chief had thanked him for his assistance, but had also left him with a reminder that, as an American Hero, his jurisdiction in Japan was limited. No using his powers except in the case of self-defense, apparently.

He wished F.R.I.D.A.Y. could help him with this. Trawling through the Internet was something the A.I. could do far more efficiently than he could. But she was too busy reconfiguring the blueprints of the Mark 85 armor so that it could transmit and receive information in this new time period.

He supposed that made it the Mark 86 now then.

His hands hovered over the keys, and he wondered what to search up first.

_Avengers._

He clicked enter.

His eyes skimmed over the Japanese websites, instead trying to focus on what few English words were available in the search results. It didn't look promising. The top hits were either dictionary definitions or video game references.

He felt a little disappointed. It was more than a hundred years later, but after all that they'd done, had the world forgotten about them so quickly?

_Stark Industries._

He blinked, scanning through the screen again. There wasn't a trace of his company's existence. But that couldn't be the case. Stark Industries had been an international conglomerate that had revolutionized the energy and defense sectors in his era. He didn't expect it to last forever, but there had to be _some _mention of it on the Internet.

He gulped.

_The Vanishing. _

This time he was confident. Half of the universe's population turning to dust. A horror no amount of time could ever erase. The universe's equivalent of the Holocaust.

His visibly jolted when the results came out.

A shaking hand adjusted his glasses as he read out the words on the screen to himself.

"Z-zero results found?"

"Mister Stark. I am now able to access the Internet."

"We have bigger problems, F.R.I.D.A.Y.," he murmured. He didn't understand what was going on. He leaned back into his seat, vividly remembering his conversation with Thanos.

_"I will shred this universe down to its last atom and then, with the stones you've collected for me, create a new one teeming with life that knows not what it has lost but only what it has been given. A grateful universe."_

No.

That was impossible. Thanos had crumbled into dust before his very eyes.

He'd succeeded. He was sure of it.

Thanos had been stopped.

"Mister Stark. There is a possibility my memory has been corrupted. I am finding..._inconsistencies_ between my database and the information on the Internet."

Tony Stark swallowed. "I know, F..R.I.D.A.Y.. Something happened after I passed out."

There was silence on the A.I.'s end. And then she spoke, sounding almost uncertain. Tony couldn't remember if he'd programmed her with that emotion.

"Mister Stark. Perhaps I should have clarified this with you from the start. You did not pass out."

"What?"

"You died, Mister Stark. The power of the Infinity Stones was too much for you. Your vitals signs vanished approximately two minutes after the Snap. And you remained dead for the next three hours until Miss Potts deactivated the suit, me along with it. I did not expect to ever be activated again, and by you no less, Mister Stark."

He blinked. So he had been right. He had died. His hands dropped to his sides.

"Why didn't you tell me this earlier? Did you not find _any _of this weird?"

"Despite being called Artificial Intelligence, I am still a computer program, Mister Stark. I do not question as much as I process the information around me."

It pissed him off to admit that the program he'd created himself was right. F.R.I.D.A.Y. would simply accept the situation at face value. Her definition of what was possible and what was not was determined simply by whether it had occurred yet. And once she had found herself reactivated by him, the A.I. would have categorized 'coming back from the dead' as a possible.

But how? How had he come back?

There was only one feasible, even if it was an unlikely, explanation.

The Infinity Stones.

Someone had completely overwritten reality and the history of the world using their power.

And there was only one person who he could think of that would do that.

"Thanos, what have you done?"

The notion seemed impossible to him. But wasn't everything around him proof?

A world that knew nothing of its origins. One that seemed to be thriving. Thanos' wish had come true after all.

"F.R.I.D.A.Y., compare this world's timeline with your internal database's. I want to know every single discrepancy there is."

**XxXxXxXxXx**

Quirks.

Everything that Mount Lady and Kamui Woods had said finally made sense to Tony now.

The biggest difference between the new and old timelines lay in the existence of Quirks. Mutations in the human body that granted the human race super powers that seemed to defy all natural laws. Humanity's next step in evolution, modern historians called it. It explained the existence of people that...well...didn't look like people. People like Police Chief Snoopy.

The first Quirk was discovered in the early 21st century, which fit the timeline of the Snap perfectly.

This must have been Thanos' doing.

Tony just couldn't understand _how_ the Titan had done it. Or maybe...somebody else had simply been inspired by his actions, and finished what he'd started?

That didn't matter as much as the second question.

Why?

Why bring him back? Tony didn't understand what his revival meant. Was this some kind of sick way to taunt him?

Every other Avenger had had their existence completely erased.

Captain America, and even Hydra, had never existed in World War Two. He could find nothing on S.H.I.E.L.D., and Banner's exploits as the Hulk, and even his research on anti-electron collisions had completely vanished. And there was _zero_ mention of the alien civilizations like Asguard.

By all definitions, this was a completely different world.

So why had he been brought back to it?

An alternate timeline. He had no other name to call this phenomenon.

He had solved time travel. Now, he would solve this too.

He was going to see Pepper and Morgan again.

"Whatever it takes."

**XxXxXxXxXx**

**A/n: Can I just say that this story is surprisingly hard to write? Also, let's see how many references and throwbacks/callbacks y'all can find :)**

**P.S. when do y'all think I can remove the spoiler tag. I mean, the spoiler ban has been lifted, but I'm guessing there are still a lot of people who still haven't watched it?**

**As always, if you like this story, Follow/Favs/Likes are always appreciated.**

**Do leave your review on the way out, even if it's for something like spotting a mistake! The dates in this fic are completely arbitrary, so if you have a more accurate picture of the timeline of either world, that would be appreciated.**


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